When John Delaney, the Football Association of Ireland chief executive, sat down in a London hotel with Martin O'Neill last week, he was expecting tough negotiations. He was prepared to compromise and was prepared to stump up plenty of cash, with the businessman Denis O'Brien once again agreeing to fund the new management team's salaries. He was not expecting O'Neill to suggest Roy Keane as his No2.

It was clear from the moment Giovanni Trapattoni was sacked in September that O'Neill was the FAI's first choice replacement. But with O'Neill known for taking his time over decisions, the association then claimed it had 'cooled' its interest and was looking elsewhere.

O'Neill wanted another shot at the Premier League, redemption after his acrimonious departure from Sunderland, but after meeting with Crystal Palace in the early part of last week, his mind changed and the Ireland deal was completed in the space of four days.

However, nobody could have imagined him wanting to bring Keane on board. They have known each other for some time and, although they would not be classed as close friends, they have an abundance of respect for each other. Keane was delighted when the offer came and had little hesitation in accepting it.

The plan was to announce the appointment later in the week but with O'Neill and Keane in Spain as part of ITV's Champions League coverage on Tuesday night, the FAI was adamant that it would be confirmed before they appeared on TV. The pair will cost around €2m per annum, with O'Brien contributing the bulk of that. Additionally, large bonuses for qualifying for tournaments are also understood to be part of the agreement.

For the FAI, selling tickets holds such importance that it delayed the announcement of the Latvia friendly until it was certain a new manager would be in place in time. With the association in a dire financial state, there is as much onus on putting bums on seats at the Aviva Stadium as there is on achieving success on the pitch. Good results, of course, lead to more interest, but with Keane's involvement, the attention placed on mundane friendlies will be heightened to a level that will reap considerable financial benefits for the association.

A press conference will be held on Saturday to unveil the partnership, fittingly hours after Sir Alex Ferguson – whose criticism of Keane left the former Manchester United captain irate – will have spoken in Dublin on the latest leg of his book tour. The Irish media will have more interest in hearing the thoughts of the assistant rather than the manager come Saturday and it is not ludicrous to suggest that it will be like that throughout their time in charge.

Few Irishmen polarise opinion like Keane. Eleven years on, the wounds from Saipan have yet to fully heal for some (the small Pacific island was trending on Twitter this morning), while Keane's stoking of the flames during Euro 2012, when he criticised players for praising supporters after their own abject performances, only served to dig up the past.

At least two squad players are understood to have mild concerns about working under Keane, but it cannot be underestimated how important this role will be in terms of re-establishing himself as manager. Ferguson's comments will have hurt and his immediate acceptance of an assistant role could be taking as an indicator of how much his stock has fallen.

The dynamic will be fascinating. Typically, the assistant manager soaks up the grievances of players, but it is difficult to imagine an Ireland player knocking on Keane's door to complain about, say, training conditions or the quality of footballs being used.

Then again, his ferocity can reap benefits and players will be determined to play out of their proverbial skin to impress. O'Neill on the other hand is a deep-thinker and will assume the role of good cop.

It will be stressed that they are not joint managers, so it will be fascinating to see how much of a role Keane has in terms of team selection. Will it be a case of O'Neill consulting Keane for advice when he has a dilemma over which central midfield pairing to go for? Or will it extend to Keane suggesting his own formation and style of play? Keane, as Ferguson intimated, wants things to be done his way, behind-the-scenes disagreements will be a given. How they overcome that and reach a satisfactory and reasonable conclusion could determine whether the partnership is a success or not.

Immediate concerns over which one would take the coaching duties – both have laissez-faire attitudes on the training pitch – will be answered by the appointment of Steve Walford, one of O'Neill's lieutenants at Leicester City, Celtic, Aston Villa and Sunderland, after further discussions between O'Neill and Delaney are held this weekend.

But with the squad assembling next Monday before the friendlies with Latvia and Poland, O'Neill will take charge of coaching duties. The squad for those games has not yet been announced, though Noel King, the caretaker in charge against Germany and Kazakhstan in October, had been preparing an extended squad list in advance of the appointment.

The reign of every Republic of Ireland manager has ended in tears and it is hard to imagine this going any other way. But for the time it lasts, every press conference and game will be scrutinised closer than ever before. The so-called 'Dream Team' are in place, take your seats on the rollercoaster.